1. Field of the Invention
The present invention generally relates to the field of safety devices for manholes. More particularly, the present invention relates to the field of manhole cover systems used in connection with underground electrical systems.
2. Description of the Prior Art
Specifically, when a power distribution system in a manhole fails, electrical failure and buildup of gases can cause an explosion in the manhole. In such an event the manhole cover is hurled high in the air, which is likely to cause damage or loss of life due to the manhole cover. To prevent this from happening, prior art provision was made whereby when such an explosion occurs the manhole cover is limited in its upward movement, with means being employed to prevent it from being hurled into the air. The prior art approach is to restrain the manhole cover while relieving the pressure caused by an explosion. The disadvantage with this prior art approach is that the casting or the neck section will be taking the entire load, which is not sufficient to hold the load. The prior art designs cannot take the force of an explosion resulting from an electrical arc at voltages above 110,000 volts.
The following eight (8) prior art patents are found to be pertinent to the field of the present invention:
1. U.S. Pat. No. 1,071,577 issued to Rego on Aug. 26, 1913 for xe2x80x9cDevice For Preventing Blowing Off Of Manhole Coversxe2x80x9d (hereafter xe2x80x9cthe ""577 Rego Patentxe2x80x9d);
2. U.S. Pat. No. 1,717,364 issued to Borland on Jun. 18, 1929 for xe2x80x9cSafety Device For Manhole Covers Or The Likexe2x80x9d (hereafter the xe2x80x9cBorland Patentxe2x80x9d);
3. U.S. Pat. No. 2,009,132 issued to Gehris on Jul. 23, 1935 for xe2x80x9cManhole Constructionxe2x80x9d (hereafter the xe2x80x9cGehris Patentxe2x80x9d);
4. U.S. Pat. No. 2,025,839 issued to Woods, Jr. on Dec. 31, 1935 for xe2x80x9cManhole Closurexe2x80x9d (hereafter the xe2x80x9cWoods Patentxe2x80x9d);
5. U.S. Pat. No. 1,955,018 issued to Rego on Apr. 17, 1934 for xe2x80x9cSafety Device For Manhole Coversxe2x80x9d (hereafter xe2x80x9cthe ""018 Rego Patentxe2x80x9d);
6. U.S. Pat. No. 2,553,934 issued to Olyott on May 22, 1951 for xe2x80x9cManhole Cover Constructionxe2x80x9d (hereafter the xe2x80x9cOlyott Patentxe2x80x9d);
7. U.S. Pat. No. 4,514,931 issued to Beck et al. on May 7, 1985 for xe2x80x9cSecuring Device For Manhole Coverxe2x80x9d (hereafter the xe2x80x9cBeck Patentxe2x80x9d); and
8. U.S. Pat. No. 5,344,253 issued to Sacchetti on Sep. 6, 1994 for xe2x80x9cAdjustable Manhole Coverxe2x80x9d (hereafter the xe2x80x9cSacchetti Patentxe2x80x9d).
The ""577 Rego Patent discloses a device for preventing manhole cover from blowing off. The cover has a plurality of downward extensions with opening therethrough, in which a nut is positioned. Secured to the wall of the manhole are guide members, through which reciprocating rods extend, with the upper end of each rod threaded to the nut. The lower end of each rod has a head and there is a guide member spaced apart from the head with a helical spring surrounding the rod member interposed between the guide member and the head. Each rod has a shoulder which limits the downward movement of the rod in the guide members when the rods are disengaged from their nuts. While the parts are in position and when gases accumulate in the manhole, the cover would be raised sufficiently against the tension of the springs to permit escape of the gases, after which the springs would return the cover to its normal closed position.
The Borland Patent discloses a safety device for manhole covers or the like.
The Gehris Patent discloses a manhole construction.
The Woods Patent discloses a manhole closure.
The ""018 Rego Patent discloses a safety device for manhole covers. The cover is adapted to close the manhole which has recesses formed in the sidewall. A tubular member is disposed in each recess, with its upper end secured to an annular seat. The tubular member has a partition, where the lower end has a closure. A piston is adapted to reciprocate within the tubular member and is located between the closure and partition. A helical spring is located between the partition and piston, where the piston is threaded to the lower end of a rod extending upwardly through the partition and having at its upper end a nut extending through the cover. The piston can be adjusted lengthwise of the rod to vary the tension of the spring and then locked in adjusted position by nuts. Surrounding the tubular member are anchors extending outwardly between the bricks forming the walls of the manhole, thereby preventing any upward movement of the tubular member. When an explosion takes place within the manhole, the cover is raised from its seat to a limited distance, such that the springs are being compressed during this upward movement of the cover. During the lifting of the cover, the gas within the manhole will escape and then the springs will return the cover to its normal position. During the lifting of the cover, the disk will operate a movable member of the switch to illuminate a lamp and signal that an explosion has occurred.
The Olyott Patent discloses a manhole cover construction. It comprises a cover supported by a seat element which is separate from a housing. The seat element has a seat portion on which the cover rests. The seat element is normally supported by inwardly projecting lugs which are provided by the housing. The seat element has a plurality of pins, where each pin is provided at its lower end with a head. The pins extend loosely through the projecting lugs. Situated between the head of each pin and the corresponding projection is a spring which encircles the pin. The seat element is releaseably secured to the manhole and whenever an abnormal pressure develops within the manhole, the seat element will raise in order to vent the manhole.
The Beck Patent discloses a securing device for a manhole cover.
The Sacchetti Patent discloses an adjustable manhole cover.
It is highly desirable to have a very efficient and also very effective design and construction of a manhole restraining system for venting out explosive gases in a manhole, thereby eliminating the damage cause by flying manhole covers. It is desirable to provide a manhole restraining system for venting out explosive gases in a manhole in a much more efficient way. It is also desirable to provide a manhole restraining system which prevents the buildup of explosive gases caused by an electrical failure in the manhole.
The present invention is a manhole restraining system used for venting out explosive gases in a manhole caused by an explosion.
The manhole restraining system comprises a main support frame, a two inch thick plate member positioned on top of the support frame, a plurality of restraining assemblies and a manhole cover for covering the manhole. The support frame and the plate member are embedded into a street and positioned above the manhole, where openings are aligned with the manhole. Asphalt covers the plate member and the support frame. Three retaining assemblies are positioned on opposite sides of the manhole cover. Each retaining assembly includes a rod, a stop plate, a coil spring, a support plate and a nut. The rod extends downwardly through the dirt and the horizontal concrete base ledge, where the stop plate, the coil spring, the support plate and the nut are positioned and secured to the other end of the rod. A PVC pipe is provided with the rod for allowing the rod to move smoothly up and down without any friction.
When an explosion occurs in the manhole, the pressure caused by the explosion lifts the plate member from a seated position on the main support frame above the manhole which in turn moves the rod, the stop plate, the coil spiring, the support plate and the nut, where the explosive gases are vented between the plate member and the main support frame. What happens is that the plate member is lifted up from the main support frame, where it breaks away from the asphalt which allows the gases to escape from the manhole. The stop plate, coil spring, the support plate and the nut absorb most of the energy caused by the explosion. The spring means soften the impact and helps bring the plate member back down to the main support frame in alignment with the manhole.
It is an object of the present invention to provide a manhole restraining system for venting out explosive gases caused by an explosion in the manhole, thereby eliminating the damage caused by a flying manhole cover.
It is also an object of the present invention to provide a manhole restraining system which includes a plurality of restraining assemblies, where each restraining assembly includes a stop plate, a coil spring, a support plate and a nut which absorb most of the energy caused by the explosion.
It is an additional object of the present invention to provide a manhole restraining system, where the coil springs soften the impact and assist in bringing the plate member back down to the main support frame in alignment with the manhole.
It is a further object of the present invention to provide a manhole restraining system for limiting the upward movement of the manhole restraining system when an explosion occurs in the manhole.
Further novel features and other objects of the present invention will become apparent from the following detailed description, discussion and the appended claims, taken in conjunction with the drawings.